1. Field of the Invention
This invention relates to a recording medium, data transmission apparatus, data receiver, and optical disk unit, and is particularly applicable to a system which transmits video data and other data or records them on an optical disk in a predetermined block unit. This invention permits each frame to be easily and correctly located by providing unique combinations for at least contiguous synchronization patterns or contiguous synchronization patterns with one synchronization pattern interleaved therebetween.
2. Description of Related Art
In a conventional optical disk unit, on the basis of synchronization patterns inserted between contiguous pieces of data, a clock out of synchronization is corrected so that the data can be correctly reproduced. Further, the optical disk unit is constructed so that the use of a combination of a plurality of types of synchronization patterns, which are fewer than the number of frames constituting one sector, helps to effectively avoid an increase in redundancy due to the synchronization patterns as well as to locate the frames on the basis of the result of reproducing the synchronization patterns.
Namely, a DVD (Digital Versatile Disc), an optical disk unit of this sort, for example, transforms video signals and audio signals successively inputted into digital signals to produce digital video signals and digital audio signals. Further, the optical disk unit subjects the digital video signals to data compression in accordance with a format defined in MPEG (Moving Picture Experts Group) and multiplexes them with the digital audio signals similarly subjected to data compression (hereinafter, the multiplexed data is called AV data), and then performs a scramble process.
Further, as shown in FIG. 15, after adding identification data indicating an address and other data to the AV data, the optical disk unit splits the AV data in a predetermined block unit, adds an error correction code, preamble, postamble, etc. to each block, generating one cluster of data from the data of these blocks. By this process, the optical disk unit records and reproduces AV data on and from an optical disk in units of error correction blocks consisting of one cluster. In FIG. 15, the number of frames is represented by the symbol Fr.
Further, the optical disk unit forms 16 sectors of data from one cluster of data, and as shown in FIG. 16, forms 26 sync frames of data from data of each sector. Each sync frame is formed with synchronization patterns SY0 to SY7 assigned to AV data or other data formed in units of 91 bytes.
In these DVDs, eight types of synchronization patterns SY0 to SY7 (hereinafter, referred to as first to eighth synchronization patterns) are successively assigned to the sync frames in a predetermined order. Namely, each sector begins with the first synchronization pattern SY0 to indicate the start of the sector, followed by the first sync frame consisting of ID data and other data. In the sector, the sixth synchronization pattern SY5 follows to form a sync frame with AV data and other data.
Further, the sector has the remaining 24 frames divided into three blocks, which have even frames assigned sixth, seventh, and eight synchronization patterns SY5, SY6, and SY7, respectively. The odd frames of each block are assigned second to fifth synchronization patterns SY1, SY2, SY3, and SY4 in this order.
With this arrangement, in a DVD, the synchronization patterns SY5, SY6, and SY7 of even frames help to distinguish among the first block, middle block, and last block of each sector, and the synchronization patterns SY0 to SY4 of odd frames help to identify a frame in each block, thereby making it possible to restore the data to be successively reproduced.
By this arrangement, in an optical disk unit of this sort, there are cases where data is reproduced from middle frames of a sector by a seek operation. Also, middle frames may not be correctly reproduced because of the occurrence of an out-of-synchronization condition due to a damage. To provide against such a circumstance, when data is to be reproduced from middle frames of a sector based on the result of reproducing synchronization patterns, the optical disk unit is constructed so that reproduction results can be outputted by correctly placing the data of frames successively reproduced even when the middle frames cannot be correctly reproduced.
Meanwhile, when the synchronization patterns SY0 to SY7 are assigned in this way, as shown by the arrow A, when data of a third frame of each sector is reproduced from data of a second frame, the sixth and second synchronization patterns SY5 and SY1 are contiguous. Also, as shown by the arrow B, when data of an eleventh frame is reproduced from data of a tenth frame, similarly, the sixth and second patterns SY5 and SY1 are contiguous.
Accordingly, in an arrangement of the synchronization patterns, when the sixth and second synchronization patterns SY5 and SY1 are contiguous, it is difficult to locate a frame from the sixth and second synchronization patterns SY5 and SY1 alone; eventually, it is difficult to correctly determine a frame until a synchronization pattern which follows is detected. Namely, it takes a long time to correctly locate a frame.
When the synchronization pattern of an odd frame of synchronization patterns that are contiguous in a stream of even, odd, and even frames could not be correctly reproduced, it can be determined which of the first, middle, and last blocks of a sector the frame exists in, but it is difficult to determine the specific location of the frame within the block; also in this case, it is difficult to correctly identify the frame until a synchronization pattern which follows is detected.
Namely, for example, if the second synchronization pattern SY1 cannot be correctly reproduced when the sixth, second, and sixth synchronization patterns SY5, SY1, and SY5 are contiguous, in FIG. 16, it is difficult to locate a specific sector in one of the following cases: when the sixth, second, and sixth synchronization patterns SY5, SY1, and SY5 are contiguous, when the sixth, third, and sixth synchronization patterns SY5, SY2, and SY5 are contiguous, when the sixth, fourth, and sixth synchronization patterns SY5, SY3, and SY5 are contiguous, and when the sixth, fifth, and sixth synchronization patterns SY5, SY4, and SY5 are contiguous.
Even when three contiguous synchronization patterns can be detected, if any of them is incorrectly detected, eventually, no correct frame can be located; also in this case, it is difficult to correctly identify the frame until a synchronization pattern which follows is detected.
In this case, one possible method is to assign a unique synchronization pattern to each sync frame, but this requires that the bit length of the synchronization pattern be longer accordingly, posing a problem in that redundancy is increased because of the synchronization patterns.